1. Field of the Invention
This invention relates to a method and a device for coating a substrate with a film. More particularly, this invention relates to a suitable method and device for coating a substrate with a thin film of an oxide of silicon, a nitride of silicon and an oxynitride of silicon.
2. Description of the Prior Art
The vacuum deposition method, the reactive sputtering method, the plasma CVD method and the like by which coating a substrate with the film is effected in a low pressure vacuum chamber, have been known as prior art. However, if a dielectric thin film of the silicon oxide film, the silicon nitride film, the silicon oxynitride film and the like, is to be formed, the plasma CVD method excels the other methods in film forming rate and in quality of the film.
The prior plasma CVD method was performed using the D.C. glow discharge, the high frequency glow discharge, the microwave discharge etc. as plasma sources. Incidentally the plasma density of the glow discharge is 10.sup.8 to 10.sup.11 ions/cm.sup.3. Therefore, there is a problem that the plasma density is too small for increasing both the utilization efficiency (yield) of a material gas and the film forming rate. On the other hand, although a high density plasma may be generated by the microwave discharge, the microwave discharge is unsuitable for generating a spacious plasma whereby coating a spacious area substrate of, for example, approximately one square meter may be effected.
Nevertheless, a plasma CVD method where a magnetic field applying external means transforms this plasma into a sheet form, is disclosed in the Japanese Patent Tokkai Hei 3-215671 based on that the plasma density of an arc discharging plasma generated by a composite cathode type plasma gun described in "Vacuum (Shinku)" Vol. 25, No. 10 (1982), is as high as 10.sup.13 to 10.sup.14 ions/cm.sup.3.
In the method which was disclosed in the Japanese Patent Tokkai Hei 3-215671, a pump capacity for exhausting the air from a vacuum chamber must be high since the size of a box type gas supplying nozzle equipped in the device is the same as the area of the plasma; therefore, the device is unfavorable due to its high price.